In general, it is really stressful working in iBanking. If you want to know the reasons why, I would first describe the job functions within iBanking:

An investment bank have a few business lines. Job functions include, Equities sales/research, Fixed Income, FX, Commodities and the Corporate Finance team. Typically when we say Investment Banking we are referring to the corporate finance, DCM/ECM employees.

Equities Research / Corporate Finance have very long hours. Workload is heavy and whilst tasks are not complex, work is very tedious and we have to check, check , check every single detail. Aside from the fact that everyone is in a hurry to meet dateline/timelines, the general culture in an IB is not forgiving. Your mind and body is constantly tired and yet you need to maintain a high level of accuracy and concentration throughout the long day. If you make a mistake (e.g. link cells wrongly, miss a decimal point, etc etc there are alot of possibilities for things to go wrong), you are lucky if you seniors catch it (you'd just get scolded badly) but if it gets public (or sent to client) and there is a material error, you can lose your job or worse get into real legal trouble.

Sales & trading have the typical stress related to sales jobs. However the product you are selling is quite complex plus there is alot of time-pressure. Work is intense and mistakes (e.g. quoting the wrong spread) directly impact the P&L and real losses can be in the millions. You need to mantain a high level of alertness, concentration.

Then, there is job security. In downturn, investment banks tend to cut staff fast. Compensation also varies greatly during cycles. All these adds to the job stress.